1. Field of the Invention
The present invention relates to a vibration wave motor which excites a vibration member by using an electromechanical transducing element to drive a movable member coupled to the vibration member.
2. Description of the Prior Art
Many proposals have been made on the vibration wave motor. A principle of the vibration wave motor is shown in FIG. 1. Numeral 1 denotes an elastic member which is a vibration member and excited by a piezo-electric device or electrostrictive device (not shown) to generate a travelling wave on a surface of the elastic member 1 as shown. Considering a mass point a on the surface of the elastic member, it vibrates longitudinally and laterally and makes an eliptical motion as shown. Numeral 2 denotes a rotor which is press-contacted to the elastic member 1 at a pressure P and driven in a direction of an arrow A by a lateral motion component of the eliptical motion of the mass point.
An amplitude of the eliptics which is a locus of motion of the mass point is very small such as several microns to several tenths microns. Thus, it is necessary to precisely finish the contact areas of the elastic member 1 and the rotor 2.
The contact area is slightly deformed by the pressure applied to contact the rotor 2 to the elastic member 1. Thus, it is difficult to attain uniform contact over the entire contact area. As a result, motor efficiency is lowered and noise is generated.
In order to resolve the above problems, Japanese Unexamined Patent Publication No. 178987/1984 discloses an approach in which the rotor is divided into a plurality of sections which are independently contacted to the contact areas. The disclosed technique is incomplete because when the vibration generated in the vibration member includes a torsional component, the rotor is obliquely contacted to the elastic member by the torsional component. Therefore, uniform contact of the elastic member and the rotor over the entire contact area is not attained.
Japanese Unexamined Patent Publication No. 188381/1984 discloses a vibration wave motor which comprises a slider constructed by dividing a rotor and a rubber elastic member for supporting the slider. In the disclosed technique, since the slider is supported by the rubber elastic member, the slider may be inclined in any direction. Thus, when the slider is driven by the lateral motion component of the eliptical motion of the mass point of the elastic member, the motion component is absorbed by the rubber elastic member as the slider is inclined so that torque is not effectively transmitted.